Standoff or proximity optronic fuse

ABSTRACT

An optronic fuse of the standoff or proximity type, which comprises an arrangement for the measurement of a transit time between a transmitted and from a target reflected pulse.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part application of Ser. No. 09/866,969; filed on May 29, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an optronic fuse of the standoff or proximity type, which comprises an arrangement for the measurement of a transit time between a transmitted and from a target reflected pulse.

[0004] In essence, the standoff or proximity fuses, at a specified approach to a target object which is to be attacked, are adapted to activate a warhead. Usually, the initiation of the triggering or detonation is implemented when the echo travel time of an optoelectronic pulse which is emitted by the fuse corresponds precisely with a specified reference time which is in conformance with the triggering distance, and which can be derived from the transmitting signal, for example, through a delay line or through a phase shifting circuit. In contrast with the prior art, there is no comparison of mutually displaced echo pulses from specified mutually adjacent fixed target distances. To the contrary, the invention relates to a continuous, extremely rapid and extremely precise measurement of a traveling or running time of a target echo pulse which is variable during the course of approaching to a target.

[0005] 2. Discussion of the Prior Art

[0006] Sepp et al., U.S. Pat. No. 5,601,024, which corresponds to German Publication DE 39 37 859 relates to the spatial and thereby timewise offset of two constructively fixedly specified laser reflection zones. In contrast with the present invention, this publication does not provide either a count sequence, nor does it disclose an echo travel time determination, and also does not provide a continuous distance measurement during approach to a target. Basically, the publication relates to evaluating two reflective regions which are mutually offset in the direction towards the target. Each region (the intersecting point of the characteristics of a laser transmitter and a light receiver) only delivers an echo when a reflected target is just located in that region. The two timewise mutually offset echoes from almost the same distance to the target are distinguished from each other by different sign digits, such as plus or minus signs. Thus, when the plus (+) signal and the minus (−) signal are at a specified relationship to each other, and moreover, evidence a specified offset in time, then one of these two target echoes characterizes the triggering approach of a real target, and the triggering or detonation is initiated. This concept is clearly contrary to the measuring process pursuant to the present invention which does not relate to any comparison between mutually offset echo pulses from fixedly specified mutually neighboring target distances. As indicated, the invention relates, to the contrary to an continuous extremely rapid and extremely precise measurement of the running or travel time of a target echo pulse which is variable during the course of approaching of a target.

[0007] German Publication DE 24 56 162 C2 discloses a missile fuse with an optoelectronic measuring device which operates in accordance with the basic principle and which, upon reaching a given range between the missile and a target surface, delivers a signal to an evaluation circuit, wherein the measuring device has a transmitter which emits optical pulses at a pulse repetition frequency through a lens and a receiver which is arranged at a given spacing from the transmitter and which records portions of those optical pulses, which are returned from the surface by way of a further lens, with a narrow-band filter which is tuned to the pulse repetition frequency and a receiving amplifier. To eliminate the effects of circuitry-induced frequency deviations, connected between the band pass filter and the transmitter is a regulating circuit by which the pulse repetition frequency of the transmitter tracks the center frequency of the bandpass filter. The input signal of the regulating circuit is a signal, which is filtered out of the noise level of the receiving amplifier by the band pass filter.

[0008] An optical range sensor for a missile fuse which operates on the basis of the pulse reflection principle and which in the reception branch has in series an amplifier, a gate circuit which is opened in the transmission pulse cycle, an integrating capacitor circuit and a threshold switch, is known from DE 26 08 066 C2. In that case, arranged in the reception branch upstream of the gate circuit is a high pass filter whose limit frequency is slightly below the transmission pulse repetition frequency. The integrating capacitor circuit serves to sum positive and negative signal components in accordance with the sign thereof.

[0009] An optronic fuse is also known, for example from the disclosure of German Publication DE 39 27 819 C2; which is, however, not applicable to the present inventive concept.

[0010] For many weapon systems which are predominantly equipped with an intelligent sensor arrangement, it may be desirable to trigger the warhead at an optimum operative range which is dependent upon the respective applicable type of target. The optronic fuses which are to be used for that purpose must be capable of offering the weapon system more than a detonation range. It is preferred if the weapon system can at a short notice in a stepless manner freely program the detonation range which is required for that purpose. That means that the fuses may not involve a fixedly specified detonation range, and must be capable of handling a large signal dynamic range.

[0011] Heretofore, detonation triggering has been essentially effected by a comparison of the echo transit time with a fixedly set reference time, for example, by means of a delay line or through a phase shifting process.

[0012] The object of the present invention is to provide an optronic fuse of the kind set forth in the introductory portion of this specification, in which the detonation range which is essentially desired can be freely programmed in a stepless or continual manner at short notice, while a very extensive signal dynamic range can be readily handled.

SUMMARY OF THE INVENTION

[0013] In the instance of the optronic fuse according to the invention, initiation of a detonation or triggering is effected not by a comparison of the echo transit time with a fixedly predetermined reference time, such as for example, by means of a delay line or by a phase shifting process, but rather by a true stepless time measurement. In that case, the echo transit time is measured with a time-digital converter. For example, fast counters are readily available for that purpose, in essence, as time-digital converters. Another possible option which is afforded is that of using components which operate with an addition of very small gate passage times. In accordance with the invention, triggering o a detonation is effected by a comparison between the respectively current or present counter state and the programmed counter state. In order to be able to process the large signal dynamic which occurs in the case of a variable extent of ranges, it is preferred if a variable gain amplifier (VGA) is incorporated into the signal processing chain, upstream of the time-digital converter. For that purpose, the VGA is capable of compensating for the range dependency of the signal, insofar as a suitable gain factor is derived from the current time measurement. That, in effect, advantageously enables that the signal evaluation only has to be capable of processing the dynamic range of the target reflectivity.

[0014] Pursuant to the invention there is solved the task to so further develop a fuse of the type as generally known in the technology, such that also within the framework of weapon systems which are equipped with intelligent sensor arrangements, the fuse can be advantageously employed, in which the type of target can be readily recognized by a sensor and the warhead is to be triggered at an optimum effective distance which is dependent upon the type of target against which it is to be defended. This is no longer realizable with fixedly specified reference values for the attainment of a distance for initiating triggering, and also not possible with theoretically contemplatable suitable reference distance measurement transmitters. To the contrary, it is advantageous to be able to attain the optimum distance for triggering within a short period of time in a stepless manner in a freely programmable (namely variable) manner, which in any event requires that a large dynamic region is to be controlled during the signal processing.

[0015] The foregoing object is thus inventively attained by the novel features in that the initiation of the triggering is no longer obtained through a comparison of the actual echo traveling times with a reference time period, for example, through a delay line or through a phase shift or displacement, but rather in a manner as through a continual time measurement in a counter which is to be designated as a time-digital-converter. In order to be able to avoid the highly complex circuitry for extremely rapid count steps in the interest of obtaining the finest possible distance resolution, pursuant to a modification of the present invention there can be incorporated into the time measurement the adding of the smallest or minutest gate passage time.

[0016] In any event, inventively the triggering is initiated through a comparison of the actually specified (programmed) count condition with the actually attained count condition. Although the count condition specification is applicable over a broad distance ranges, there must be processed a large signal dynamic, as to result of which the signal processing chain possesses a travel-time dependently controlled amplifier (variable gain amplifier) VGA connected ahead of the time-digital-converter. Through the amplifier there is compensated the distance-dependency of the echo signal, inasmuch as the amplification factor is increased with the time measurement.

[0017] The triggering is initiated when a variably specified reference count condition has been reached. The counter then operates extremely rapidly when simple gate modules are connected in succession and there minimal passage times are added together. The VGA (variable gain amplifier) which is connected ahead of this time-digital-converter prevents any overcontrol, in that the signal amplitude is reduced at the reflected target pursuant to the extent of the approach thereto. For this purpose, the amplification factor of the VGA is varied by the actual count result of the travel time measurement. The signal dynamic (amplitude fluctuation of the echo signal) is thereby no longer influenced by the distance to or from reflecting target, so that the amplitude fluctuations cross the reflections at the target surface and thereby, inasmuch as the expected scenario is known, provide information pertaining to the nature of the target, with which there is actually correlated the distance to the target (reference count condition). Thereby, the warhead can be triggered in a mode adaptive to the target, namely, at a distance to the target which is optimally correlated with the actual class of targets. Without any modification in the electronic fuse circuitry, merely by a change of the reference count condition, the stand-off (in effect, the distance to the target for triggering) is optimized to the actually present class of targets, which is characterized by its reflective phenomenon.

[0018] The optical fuse for the warhead of a weapon system which is equipped with an intelligent sensor arrangement, therefore operates on the basis of the pulse transit time process and implements echo transit time measurements. In order, in the weapon system, to be able to steplessly and freely (randomly) program the desired detonation range at short notice and in order to be able to handle an extensive signal dynamic range, provided for measurement of the echo transit time is a time-digital converter, in conjunction with a thereto upstream-arranged VGA, which for example is a fast counter or components which operate with an addition of very minute gate passage times.

[0019] The advantages achieved with the invention are that the warhead combined with the optronic fuse can be fired in a target-adaptive manner, wherein a standoff universal fuse can be embodied, which can be adapted through suitably programming to any warhead without a change in the electronics, and also that a standoff universal fuse can be provided which can be adapted by programming to any position of installation of the weapon system without a change in electronics. In this last-mentioned connection reference is directed, for example, to German Publication DE 38 21 218 A1 which describes an overflying projectile for combating a target object, detected in a low search trajectory by means of a warhead on board the overflying projectile.

[0020] While the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention 

What is claimed is:
 1. An optronic stand-off fuse including an arrangement for the measurement of a transit time between a transmitted and from a target reflected pulse, said measuring arrangement comprising a fast counter with reversible count condition interrogation; and a transit time-dependently controllable amplifier being connected upstream of said fast counter.
 2. An optronic stand-off fuse as claimed in claim 1, wherein the function of said fast counter is implemented through an addition of the minutest gate passage time periods. 